When dealing with scanned color images, as with scanned monochrome images, one often has to apply a low pass filter to render a scanned image on a printer so that moiré is eliminated. This is done by descreening. The preferred way of descreening is with a circularly symmetric filter so that the same frequency occurring at any angle is descreened by approximately the same amount. A circularly symmetric response is easily achieved using a single, non-separable filter. However, it takes significantly more processing of the image data to apply a non-separable filter to image data than it does to apply a separable filter.
What is needed in this art is an application that achieves a close approximation to the desired circularly symmetric shape while requiring less processing power than is required to implement a non-separable filter.